1. Field of the Invention
The present invention relates generally to a paper feeding apparatus for threading a web through a web threading path of a rotary press. More specifically, the invention relates to a paper feeding apparatus for feeding a web in a direction of pulling upon threading the web by pulling a leading end of a series of web using of a threading member which is movably provided along the web threading path.
2. Description of the Related Art
Paper feeding apparatus as set forth above have been disclosed in Japanese Unexamined Patent Publication (Kokai) No. Hei 6-134957, Japanese Unexamined Patent Publication No. Hei 8-216363 and Japanese Registered Utility Model No. 2532047, for example.
The paper feeding apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 6-134957 is includes paper feeding roller in opposition to a web threading path, which paper feeding roller is arranged for feeding the web toward a downstream side in cooperation with a guide roller, a movable roller is provided on the downstream side of the paper feeding roller for removing slack in the web caused due to a difference of a length between an actual web threading path and a path of a web threading member, which latter path is set to be slightly longer than the former, and for providing an appropriate tension for the web.
On the other hand, the paper feeding apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 8-216363 is provided with a paper feeding roller in opposition to a web threading path for feeding the web toward the downstream side by gripping the same in cooperation with the guide roller, a detecting means is provided for deflecting the extra length of the web corresponding to the difference between the actual web threading path and the path for the web threading member which is set to be slightly longer than the actual web threading path toward the downstream side, and for detecting a deflection amount for adjusting a rotation speed of the paper feeding roller on the basis of the result of detection of the deflection amount to optimize the web feeding amount during threading.
On the other hand, the paper feeding apparatus disclosed in Japanese Registered Utility Model No. 2532047 is also provided with a paper feeding roller in opposition to the web threading path. The apparatus includes driving means for driving the paper feeding roller toward and away from a holding roller for releasably holding the web. Furthermore, a control means is provided for controlling operation of the driving means for selectively moving the paper feeding roller toward and away from the holding roller for holding and releasing the web depending upon a magnitude of slacking of the web on the downstream side of the holding roller. When no slacking of the web is present on the downstream side of the paper feeding roller, the web is depressed onto the holding roller by the paper feeding roller to feed the web toward the downstream side. On the other hand, when slacking of the web is present on the downstream side of the paper feeding roller, the paper feeding roller is released away from the holding roller to interrupt feeding of the web.
In the respective publications set forth above, the following problems to be solved are present.
Namely, since the paper feeding apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 6-134957 does not control feeding of the web toward the downstream side, when the web threading path is long, the magnitude of slacking of the web caused by the difference between the length of the web threading path and the path for passing the web threading member, which is slightly longer than the web threading path, increases progressively and thus slacking cannot be removed unless a large number of movable rollers are provided. Thus, this apparatus requires a large installation space and high production cost. On the other hand, by providing a large number of movable rollers, the construction becomes complicated, maintenance is troublesome, and reliability is low.
On the other hand, the paper feeding apparatus as disclosed in Japanese Unexamined Patent Publication No. Hei 8-216363 has been proposed to solve the problem encountered in the invention disclosed in Japanese Unexamined Patent Publication No. Hei 6-134957. However, the improved apparatus requires control means for electrically controlling rotation speed of the paper feeding roller depending upon slacking magnitude of the web caused by the difference between the length of the web threading path and the length of the path for passing the web threading member, which is slightly longer than that of the web threading path.
On the other hand, when control is not effected for smoothing variation of feeding speed of the web fed by the paper feeding roller, tension may be exerted on the web on the upstream side of the paper feeding roller intermittently and abruptly so that a take-up body may be excessively rotated by its own inertia moment to unnecessarily extract the web from the take-up body to droop and get stuck, or a rupture in the web may be caused due to an abruptly exerted tension.
Furthermore, the paper feeding apparatus disclosed in Japanese Registered Utility Model No. 2532047 is designed for controlling feeding of the web by the paper feeding roller depending upon the slacking amount of the web caused by the difference beteen the length of the web threading path and the length of the path for passing the web threading member, which is slightly longer than the length of the web threading path, similarly to the paper feeding apparatus disclosed in the foregoing Japanese Unexamined Patent Publication No. Hei 8-216363. This apparatus also requires control means for performing electrical control for paper feeding, thereby resulting in high production cost.
On the other hand, the apparatus disclosed in Japanese Registered Utility Model Publication No. 2532047 achieves feeding control of the web by intermittently depressing the web onto the holding roller using the paper feeding roller. Thus, contacting and releasing of the holding roller and the paper feeding roller may be a cause of vibration or other relatively undesirable mechanical disturbance. Furthermore, feeding control of the web by contacting and releasing of the holding roller and the paper feeding roller repeats feeding and stopping of feeding to exert tension on the web on the upstream side of the paper feeding roller intermittently and abruptly to cause excessive rotation of the take-up body upon stopping feeding by its own inertia moment to extract the web unnecessarily from the take-up body. The web may thus droop or get stuck, or a rupture in the web may be caused due to abruptly exerted tension.